GPS: A Noob's Questions

[TheDeadWalk]

Well I just got my first GPS about a week ago, and I have several questions. I bought the Garmin Etrex Venture HC. It seemed like a nice cheap GPS that would work for what I wanted it for, and so far, I have been very happy with it. I do have several questions though.

 

My first couple questions are about the Satellite screen. First, are the numbers significant? Or are they just the "name" of the satellites. Also, how do the meters work? I understand the taller the bars the better the signals but do not quite understand all that. On the same line, what does a hollow bar mean comapred to one that is filled in? My last question would be what does the D stand for inside the bars. I saw that for the first time yestereday, and am just curious.

 

My last question (I had more but since writing this have figured them out) would be about averaging. What exactly is it doing? Or is it literally just taking the location over and over and over again and just averaging it? That seems a little innacurate to me, as the average could be in a further location than even originally.

 

Thanks,

Telp

[+Tequila]

I don't believe the satellite numbers have any real signifcance to civilian users, and perhaps not to anyone. It is merely a way of relating the "meters" to the "sky" visual on that screen.

 

A colored bar means you have locked on to that bird.

 

The "D" means you are picking up the WAAS signal which should give you a more accurate position reading.

 

Not sure about the averaging but suspect the GPS is continually taking the reading and compiling them into an average. It is a very good idea. Often if you let a GPS sit at a single spot for 10 minutes, you will see a difference in the position. I would not expect anything other than the last digit to change unless it is a 9 or 0.

[+Cardinal Red]

First, are the numbers significant? Mostly, no. Just ID numbers. Other than the regular satellites are numbered 1 through 32. Anything above 32 (33 through 51) denotes a WAAS (Wide Area Augmentation System) satellite.

 

what does a hollow bar mean comapred to one that is filled in? When the GPS receiver initially locks onto a satellite, the display initially shows "hollow" signal strength bars. At this time, the Ephemeris data has yet to be completely collected (or any existing is "stale"). Once the ephemeris data is collected from EACH satellite in turn, the associated signal strength bar will turn "solid" and then that data is considered valid and available for navigation.

 

what does the D stand for inside the bars. The "D" stands for differential. Indicating that the WAAS receiver is providing "differential" position correction to that satellite. The difference is between the calculated and known position at the WAAS ground station. That correction distance is then sent back to your WAAS receiver, resulting in a more accurate position fix.

[TheDeadWalk]

Thank you all for the replies.

[+Egnix]

First, are the numbers significant? Mostly, no. Just ID numbers. Other than the regular satellites are numbered 1 through 32. Anything above 32 (33 through 51) denotes a WAAS (Wide Area Augmentation System) satellite.

 

While your answer is probably sufficient to answer the original question, I thought I'd be a geek and point out the answer isn't quite correct...

The number you see on the satellite screen is the satellite's PseudoRandom Noise (PRN) code. This number identifies the code the satellite is using in it's signal. It is not an ID number of the satellite.

A satellite's ID number is unique to that satellite, while PRN codes are obviously "re-used"

See here for more info on PRN codes.

 

See here for the current SVN (SV ID)/PRN assignments.

[TheDeadWalk]

First, are the numbers significant? Mostly, no. Just ID numbers. Other than the regular satellites are numbered 1 through 32. Anything above 32 (33 through 51) denotes a WAAS (Wide Area Augmentation System) satellite.

 

While your answer is probably sufficient to answer the original question, I thought I'd be a geek and point out the answer isn't quite correct...

The number you see on the satellite screen is the satellite's PseudoRandom Noise (PRN) code. This number identifies the code the satellite is using in it's signal. It is not an ID number of the satellite.

A satellite's ID number is unique to that satellite, while PRN codes are obviously "re-used"

See here for more info on PRN codes.

 

See here for the current SVN (SV ID)/PRN assignments.

 

'

 

This is all really interesting. Thanks for that info. Very cool.

[+Latentk]

Very intersting read, learned a lot of information from your posts! I took a GPS course that introed me to Geocaching and the intricate workings of a GPS. I love this stuff!!!!